The present invention relates to an internal combustion engine, and more particularly to a torch-ignition type internal combustion engine having a main combustion chamber connected to an intake port for an air-fuel mixture and an auxiliary combustion chamber for the torch-ignition of a charge of the mixture fed into the main combustion chamber.
Torch-ignition internal combustion engines of the type referred to above have been known in the art. This type of internal combustion engines have an advantage such that the production of harmful components during the combustion of an air-fuel mixture can be minimized. In order to effectively produce the latter advantageous effect, the internal combustion engines of the type concerned have heretofore been provided with various arrangements and constructions. The torch-ignition internal combustion engines having any of these arrangements and constructions have a common and general characteristic that the engine performance was greatly influenced by the shape of the auxiliary combustion chamber, the size and orientation of a torch aperture and a position of spark plug electrodes. The engine performance which was most influenced by the latter factors was the ignitability and torch effect.
In the prior art torch-ignition type internal combustion engines, it was usual to provide a single torch aperture at that end of the auxiliary combustion chamber adjacent to the main combustion chamber, and to dispose the spark plug electrodes at the inner part of the auxiliary combustion chamber remote from the torch aperture. Any thoughtful consideration was not made with respect to the positional relationship between the torch aperture and the spark plug electrodes.
It is the inventors' understanding that, with the positioning of the spark plug electrodes employed in the prior art, the residual gases produced during a combustion stroke and retained in the auxiliary combustion chamber were forced into the inner part of the auxiliary combustion chamber by an air-fuel mixture introduced through the torch aperture into the auxiliary combustion chamber by the upward movement of the piston on a compression stroke; thus, at the time of ignition, the residual gases were retained in the inner part of the auxiliary combustion chamber forming a stratum in the vicinity of the spark plug electrodes, which presumably adversely affected the spark-ignition of the mixture in the auxiliary combustion chamber. It was observed by the inventors that the ignitability was injured particularly during a low-load engine operation with a resultant poor engine drivability.
Further, with the positioning of the spark plug electrodes of the prior art, the front face of the combustion flame produced by the spark-ignition in the auxiliary combustion chamber proceeded from the inner part thereof toward the torch aperture on the combustion stroke. Thus, an amount of the air-fuel mixture existed in an unburnt state between the inner part of the auxiliary combustion chamber and the torch aperture was forced out of the auxiliary combustion chamber through the torch aperture before the combustion flame face reached the torch aperture, with a result that the torch effect produced was very weak or reduced.